New fields of application require the processing of polyol formulations of higher viscosity. The use of components of higher viscosity offers many advantages. In general the viscosity of polyether polyols, and in particular polyester polyols, increases distinctly with increasing functionality. In order to achieve high degrees of cross-linking, and thus a better mechanical property level, the use of relatively larger quantities and constituents of polyol components of high functionality is desirable.
As high-viscosity component, the isocyanate component is also used in the form of a prepolymer.
Satisfactory mixing in a self-cleaning mixing chamber comprising no stirring apparatus still presents difficulties to the extent to which the viscosity of such components increases. Page 175, last paragraph of the "Kunststoff-Handbuch", Vol. 7, "Polyurethanes" (published by Carl Hanser Verlag, Munich 1993), states: "Whereas the miscibility limit was previously reached at 1500 mPa.s, it is currently possible to handle viscosities exceeding 2000 mPa.s in accordance with the injection method". In reality, however, it has not yet been possible to process reaction components with viscosities above 3000 mPa.s in accordance with the counterflow high-pressure injection method. The resultant foam contains striations and the physical values fall rapidly. It has therefore been necessary to use mixing heads comprising stirring apparatus.
It was also known ("Kunststoff-Handbuch, p. 125) to reduce the viscosity at an elevated processing temperature to 2000 to 3000 mPa.s. However, the increased component temperature causes the reactivity of the systems to increase such that the foaming process can no longer be controlled.
Where the following observations relate to the polyol component as high-viscosity component, this is by way of example. The observations apply correspondingly when an isocyanate component is used as high-viscosity component.